1. Technical Field
The present invention relates to suspending and positioning metal reinforcing bars (rebar) in the footings and foundations of buildings and other structures.
2. Background Art
Pre-stressed concrete is a type of reinforced concrete that has been subjected to an external compressive force prior to the application of loads. Typical applications for pre-stressed concrete include slab-on-grade construction and the like. The compressive force in the concrete slab is typically provided by placing steel tendons within the concrete that are initially tensioned with hydraulic jacks and held in tension by end anchors secured to the foundation forms.
Pre-stressed concrete may be broadly categorized as either pre-tension or post-tension. Pre-tension refers to the method of first stressing tendons and then casting concrete around the pre-stressed tendons. The concrete cures before releasing the pre-stressed tendons and transferring the stress from the tendons to the concrete. Post-tension refers to the method of casting concrete around unstressed tendons and then stressing the tendons after the concrete has reached a specified strength.
Although the modern method of pre-stressing concrete may be traced to the late 1920's, its general use in the United States did not begin until the late 1940's or early 1950's. General acceptance and the primary increase in use occurred primarily between 1965 and 1975. Application of pre-stressing was being made in all aspects of construction including buildings, towers, floating terminals, ocean structures and ships, storage tanks, nuclear containment vessels, bridge piers, bridge decks, foundations, soil anchors, and virtually all other types of installations where normal reinforced concrete was acceptable. Thus, pre-stressed concrete and methods for its initial installation for diverse applications is now well known.
Similarly, the use of rebar in reinforced concrete structures, and in particular, concrete structures in which the reinforcing steel has a connection with surrounding earth, is well known. The typical application usually involves the placement of rebar in the footings or foundations utilized in homes, commercial buildings, or other concrete structures. The long time practice for utilizing rebar in the construction of the footing or other foundational support system for building and the like is to dig a trench in the ground and, in order to impart tensile strength to the concrete which will fill the trench and constitute the footing, suspend one or more horizontally-positioned layers of steel reinforcing bars within the trench. Additionally, rebar is used in foundation slabs and as a reinforcing means for other parts of the foundation, particularly for transferring loads from areas of lower stability to areas of higher stability.
One common practice for placing rebar in footings and foundations is to suspend or otherwise position the rebar at the proper location and orientation using pieces of wire wrapped around nails, rebar stakes and other rebar sections. In most cases, it is desirable to utilize sufficient rebar and wire to provide the necessary strength to hold the various rebar reinforcing materials in place against the force of the concrete as it is poured around the rebar to form the footings and/or foundation for the structure. This is especially the case with pre-stressed concrete where the rebar and tendons act in concert to strengthen and reinforce the concrete structure.
Although the above-mentioned practices are relatively simple to implement and generally well accepted in the construction industry, they are not without certain limitations. One of the most significant issues is the amount of time and energy that is required to suspend the rebar in place using concrete forms, nail, tie wire, etc. Since the placement of the rebar is generally a manual process, it can be very time-consuming to place and tie each section of rebar in place. Additionally, the use of wire to tie the rebar in place can provide for less than optimal stability.
In some cases, the wire is not tied securely and the weight of the concrete being poured over the rebar can cause the rebar to be dislodged and shifted out of position. Alternatively, the rebar may shift or rotate in place, further destabilizing the entire rebar support system. Finally, there may be a certain lack of uniformity and deviation from best practices in the suspension of the rebar, based on the diligence and experience of the workers suspending the rebar in place. If any of this happens, the structural integrity of the concrete foundation or structure can be comprised. Any such undesirable movement of the rebar requires an even more time-consuming operation to retrieve or remove the dislocated rebar and replace/reposition it in the desired and proper location.
Accordingly, without an improved rebar support apparatus that can properly suspend, support and position the rebar in the appropriate location and orientation, while simultaneously providing an inexpensive, quick and easy installation process that fixes the rebar firmly in place and maintains the requisite stability for the suspended rebar, the structural effectiveness associated with the placement of rebar in concrete footings and foundations will continue to be sub-optimal.